There is currently great interest in developing a new generation of heat-stable, nonflammable, high-capacity, long-lived, rechargeable batteries for various applications, including the consumer electronics and automobile industries.
Lithium-ion batteries are currently the most widely used power source in portable electronics such as laptops, cell phones, cameras and camcorders. State-of-the-art Li-ion batteries utilize graphite anodes that provide a theoretical capacity of 372 mAh.g−1. With recent technological advances, portable devices have become more compact and functionally more sophisticated. These technological attributes and the desire from consumers to increase battery operating times have driven the need for increased lithium-ion battery capacity. The development of alternative anode materials with significantly higher capacity than current graphite anodes is thus of critical importance.
Silicon is an attractive alternative to graphite due to its theoretical capacity of 4200 mAh.g−1, which is more than eleven times that of commercially available graphite anodes. However, a major challenge associated with silicon anodes is the large volume change during the lithium insertion/extraction processes. Upon cycling, lithium forms alloys with silicon, and one silicon atom can adopt a maximum of 4.4 lithium atoms with the formation of Li22Si5, which corresponds to a unit cell volume change of 400%. Such a large volume difference leads to poor cycling stability of a silicon-based anode, resulting in cracking and disintegration of the electrode. Ding, N. et al. J. Power Sources 2009, 192, 644; Kim, H. et al. Angew. Chem. Int. Ed. 2008, 47, 10151. Consequently, large irreversible capacity and rapid capacity fade are often observed with silicon anodes. Also, due to the large volume expansion of the silicon anode during cycling, about 12 to 15% of cycleable lithium can be lost in the first cycle from the surface of the anode in the formation of a solid electrolyte interface (SEI). Therefore, the main issue of improvement of Si cyclability is how to overcome the volume change.
Attempts to overcome this problem include the use of alternative binders, alternative electrolytes, and alternative anodes, such as carbon coatings on silicon cores, carbon/silicon mixtures (e.g., a silicon dispersion in a carbon matrix), and silicon nanomaterials. Id.; Baldwin, R. K. et al. Chem. Commun. 2002, 1822; Lestriez, B. et al. Electrochem. Commun. 2007, 9, 2801; Mazouzi, D. et al. Electrochem. Solid-State Lett. 2009, 12, A215.
Among silicon-based materials, silicon monoxide (SiO) is a promising candidate since it undergoes less severe volume expansion compared with silicon. SiO has been shown to have an initial capacity of 800 mAh/g, but its cycle life was limited to thirty cycles due to expansion of large particles. Present SiO anodes are fabricated by mechanochemical milling of SiO powder to reduce particle size from 10-100 microns to sub-micron (<1 um) particles to improve cycle life. However, this step does not lead to a uniform particle size distribution and this lengthy process is accompanied by contamination of active material by the ball milling media. Additionally, due to the large volume expansion of the silicon anode during cycling, about 12 to 15% of cycleable lithium is lost in the first cycle on the surface of the anode in the formation of a solid electrolyte interface (SEI).
Anodes made from silicon nanomaterials or nanoparticles can incorporate regular pores, allowing a structure's expansion without damage and loss of capacity. Cho, J. J. Mater. Chem. 2010, 20, 4009. However, silicon nanoparticles can aggregate during battery cycling, which impairs battery performance. No general solution has yet been accepted in the field as optimal.
Therefore, there is a need to develop alternative anode materials and anodes that have high thermal stability, excellent durability, long cycle life, and high charge density, as well as inexpensive, simple methods of producing the anode materials and anodes. The present invention satisfies these and other needs.